Angiogenesis (the physiological process through which new blood vessels form from pre-existing vessels) has an essential role in development, reproduction and repair. However, pathological angiogenesis occurs not only in tumor formation but also in a range of non-neoplastic diseases that could be classed together as “angiogenesis-dependent diseases” (Carmeliet P and Jain R K (2000) Nature 407, 249-257; Simons M (2005) Circulation 111, 1556-1566).
Endometriosis is a chronic disorder characterized by the implantation of endometrial glands and stroma outside the uterine cavity. Despite different hypotheses regarding the pathogenesis of endometriosis, it is widely accepted that endometriosis is an angiogenesis-dependent disorder and that angiogenesis plays an essential role in the growth and survival of endometriotic lesions (Taylor R N, et al. Ann N Y Acad Sci 2002; 955:89-100).
Endometriotic lesions require new vessel formation to deliver the oxygen and nutrient supply that are essential to the development and progression of endometriosis (Groothuis P G, et al. Angiogenesis 2005; 8:147-56). Dense vascularization is a typical pathological feature of endometriosis. Numerous peritoneal blood vessels can be observed around the endometriotic lesions during laparoscopy, and ectopic endometrium is highly vascularized under histological examination (Nisolle M, et al. Fertil Steril 1993; 59:681-4).
Animal models have confirmed that angiogenesis occurs in endometriosis by demonstrating the development of adjacent blood vessels from the surrounding vasculature into the endometriotic implants (Becker C M, et al. Am J Pathol 2008; 172:534-44; Xu H, et al. Hum Reprod 2009; 24:608-18). Anti-angiogenesis therapy offers a new opportunity for the treatment of endometriosis (Hull M L, et al. J Clin Endocrinol Metab 2003; 88:2889-99).
Current treatments for endometriosis consist of various hormonal therapies aimed at interrupting the cycles of stimulation and bleeding of endometriotic lesions. However, this approach is deemed not very satisfactory (Rice V M. Ann N Y Acad Sci 2002; 955:343-52).
Anti-angiogenesis for the treatment of endometriosis has the potential advantage of lower recurrence rates and less endocrine side effects compared to conventional surgical and hormonal therapies (Xu H, Wang C C. Endometriosis: Symptoms, Diagnosis and Treatments. Mitchell L A Ed. Nova Science, New York. Chapter 1, pp. 1-40, 2010). Common angiostatic compounds, such as VEGF antibody, TNP-470, endostatin and anginex, have significantly decreased microvessel density in the established endometriosis lesions and significantly inhibited the growth and development of endometriosis (Nap A W, et al. J Clin Endocrinol Metab 2004; 89:1089-95; Dabrosin C, et al. Am J Pathol 2002; 161:909-18; Yagyu T, et al. J Clin Endocrinol Metab 2005; 90:3017-21). To date, the only clinical trial that has been conducted was on thalidomide (Scarpellini F, et al. Fertil Steril 2002; 78:S87).
Although the results showed promising pain relief in endometriosis patients, thalidomide is a potential teratogen, which prohibits its use in women who want to become pregnant. Furthermore, anti-angiogenic agents could also serve to limit physiological angiogenesis, such as in ovulation and menstruation (Nyberg P, et al. Cancer Res 2005; 65:3967-79). These agents' possible adverse effects on reproductive functions and on offspring must be addressed in this vulnerable population (Klauber N, et al. AGM-1470. Nat Med 1997; 3:443-6; Becker C M, et al. Fertil Steril 2005; 84 Suppl 2:1144-55).
Certain compounds in Tea have been identified as having have various biological benefits. In particular, tea polyphenols are the main chemical constituents of green tea (Graham H N. Preventive Med. 1992; 21:334-50). Specifically, The polyphenols found in green tea which are composed of various kinds of catechin derivatives, mainly catechin (C), epicatechin (EC), gallocatechin (GC), epigallocatechin (EGC), epicatechin-3-gallate (ECG), gallocatechin-3-gallate (GCG) and epigallocatechin-3-gallate (EGCG), and are found to have potent anti-oxidative, anti-mitotic and anti-angiogenic properties (Nagle D G, et al. Phytochemistry 2006; 67:1849-55).
In particular, EGCG is the most abundant catechin and has the most potent biological properties among the other catechins (Lea C H, et al. Chem Ind 1957; 1073-4). The anti-angiogenic activity of EGCG has been widely demonstrated in vitro and in vivo (Cao Y H, et al. Nature 1999; 398:381). In our laboratory, we demonstrated that EGCG suppressed the angiogenesis signaling pathway and inhibited neovascularization and the growth of experimental endometriosis in mice (Xu H, et al. Hum Reprod 2009; 24:608-18; Xu H, et al. Fertil Steril 2011; 96:1021-8).
However, EGCG is notably unstable under physiological conditions and is known to have poor bioavailability (Chen Z, et al. J Agric Food Chem 2001; 49, 477-82), because it is (1) unstable in neutral or slightly alkaline conditions in the intestine and in body fluid; (2) poorly absorbed due to the high hydrophilicity of EGCG; and (3) modified through biotransformation reactions, including methylation, glucuronidation, and sulfate formation (Zhu Q Y, et al. J Agric Food Chem 1997; 45:4624-8).